In the update, Mr Marchant said it was "becoming more difficult" not to pass on the rising cost of global energy to Scottish and Southern's customers, as utility companies blame high oil prices for any increases.

"The extent of the energy shock with which the entire global economy is having to contend has been well-documented, and its full impact on prices for electricity and gas in the UK has still to be felt," Mr Marchant said.

"We are continuing to resist the pressure to put up prices for domestic customers, but doing so is becoming more difficult by the day."

The UK's big power companies raised prices of gas and electricity at the beginning of the year, sparking an investigation by the energy regulator, Ofgem.

Scottish and Southern was the last of the big six companies to increase tariffs in March.

Mr Marchant said the timing of this year's further rises would depend on the movements of the other major energy companies.

Last week, a report by energy company Centrica predicted the cost of an average household's energy bills could rise to more than £1,000 a year by 2010.

Scottish and Southern, which has gained 350,000 customers over the past year, said it was continuing to invest in "airtricity", or wind farms, as an alternative form of energy based on joint European ventures and a proposed site near Glasgow.

The Perth-based company has set a target of delivering 4pc annual growth in dividends to its shareholders.